Method for electrolytic surface modification of flat metal workpieces in copper-sulfate treatment liquid containing sulfate-metallates

ABSTRACT

The invention relates to a method for the electrolytic surface modification of a flat workpiece by the deposition of copper aggregates. The invention also relates to flat metal workpieces that can be produced using this method and to the use of said metal workpieces as substrates for the formation of secure adhesive bonds comprising a plurality of materials.

The present invention relates to a method for the electrolytic surfacemodification of a flat metal workpiece by deposition of copperaggregates. The invention further relates to the flat metal workpiecesproduced with this method and to the use of the metal workpieces assubstrate for the formation of strong adhesive bonds with a plurality ofmaterials.

The production of a large and rough surface is regarded as aprerequisite for a binder-free pressing of surfaces made of differentmaterials. Depending on the combination of materials, the surfaces arefirst of all cleaned and then structured. Structuring is effected in thecase of metal-metal bonds by dry brushing or grinding. In the case ofmetal-plastic bonds, which are generally produced by extruding a plasticonto a metal surface, the metal surface is pre-treated, e.g. byconversion, such as phosphating, chromating among other things, or themetal surface is modified by deposition of a deeply structured (“rough”)surface of a metal (treatment). In addition to these developments, inthe case of plastics, in particular bio-adapted developments are ofinterest which lead to surfaces which are covered with micro-dimensionedadhesion islands (e.g. suction feet).

In electrically particularly sensitive and chemically extremelychallenging bond systems, the use of as few components as possible inthe bonding zone is advantageous because here the release of disruptivesubstances is less likely and because the failure of the bond can bekept to a minimum.

For this reason, in the above-named areas of application, the bonds arepreferably produced from a brushed metal surface or one modified bytreatment and the desired material to be rolled, pressed or drawn on.

The production of flat continuous material (strips, foils) with such atreatment is usually effected according to the conventional method ofstrip electroplating. The technical difficulties of the methodsused—degreasing, electrolytic cleaning, pickling, coating—consist in theinsufficiently uniform edging of the surface of foils and strips. Theachievable “usual” cleanness of the surface and the locally differentroughness of the material only permit a locally preferred growth ofaggregates of the treatment on the surface.

The electrolytic coating of a metal surface with a metal or a metalalloy represents a known method for the surface treatment of a metalworkpiece, such as for example a metal strip or a sheet. For example, inthe case of electrolytic strip coating, the strip is guided through oneor more electrolytic cells. In each electrolytic cell, the strip isusually brought into a solid-solid connection with the negative terminalof a rectifier via so-called current rolls. The strip consequentlyserves as negative electrode, i.e. as cathode. As a rule, the positiveelectrode, i.e. the anode, is formed as a pair of electrodes, whereinthe strip runs through between the two electrodes.

Through the electrolytic coating, the metal workpiece to be coated isprovided with a substantially level metal coating uniformly on allsides. Even if metal workpieces having a relatively rough surface natureare used, the surface is leveled. However, for applications in whichgood adhesion to another material is required, a smooth surface may beundesirable. Good adhesion between two materials is achieved when thereis a chemical interaction and/or a mechanical engagement intopographical features of the adhesion partners. If this is not or isnot sufficiently the case, the adhesion deteriorates. Thus, pooradhesion between a metal surface and the same or a different material,for example a lacquer layer, a paint layer or an adhesive can lead toproducts which are of inferior quality or even unusable.

Various technical solutions have been developed to improve the adhesionto metal surfaces. Anodizing is known as an electrolytic process forimproving the adhesion to metal surfaces. In the case of anodizing, aregularly structured, porous oxide layer is formed on the surface of ametal workpiece connected as anode using an acidic electrolyte, such ase.g. sulphuric, phosphoric or chromic acid. The pores enable themechanical engagement of the anodized metal workpiece with anothermaterial, such as a paint, lacquer or adhesive layer. However, anodizingis limited to a few metal materials, such as for example aluminium,titanium and alloys thereof. Above all, anodizing aluminium isindustrially significant (Eloxal process; electrolytic oxidation ofaluminium). Here, an aluminium oxide layer with a porous structure formson the surface of the aluminium material.

An improvement in the adhesion can also be achieved by inserting anearlier step for the electrolytic pre-treatment of the surface to becoated. For example, before the actual cathodic deposition process, themetal workpiece can be subjected to an anodic treatment in which anerosion process is induced in which tiny particles and residues orimpurities located on the surface of the metal foil are removed and abright surface is obtained. In the subsequent cathodic treatment, adeposition/coating process is induced, in which a metal is deposited outof the treatment liquid onto the cleaned and bright surface, usually inthe form of aggregates. The anodic and cathodic polarization can beeffected in a similar way to the conventional galvanic coating throughsolid-solid contact or, in a further developed process according to theneutral conductor principle, be a contactless polarization.

In the case of all of the surface modification processes mentionedabove, the columnar shape of the deposited aggregates limits theadhesion in the bond. The adhesion in the bond improves with the numberof aggregates per unit of area. It always strives towards a thresholdvalue which consists in the tear resistance/breaking strength of theaggregates themselves. For example, through the length of theaggregates, the adhesive bond is substantially dependent on the flowbehaviour of the plastics to be pressed on, in particular when the flowbehaviour is so poor that the plastic does not reach the base of thetreatment and only undercuts form on the tips of the aggregates. Thebond can then be compared to a plastic plateau on metal stakes. Even ifsuch an adhesive bond is sufficiently good, there remain cavities in thebond at the base of the conventional aggregates of the treatment, intowhich aggressive chemicals can penetrate and can damage or destroy theadhesive bond through corrosion.

There is therefore a need for a method for improving the adhesion tometal surfaces. It is thus the object of the present invention toprovide a simple and efficient method for increasing the adhesivestrength of flat metal workpieces. A further object of the invention isthe provision of a method for modifying/converting the surface of a flatmetal workpiece by deposition of a copper layer doped with rare earthelements.

BRIEF DESCRIPTION OF THE INVENTION

To achieve this object, a method for the electrolytic surfacemodification of a flat metal workpiece is provided according to theinvention, in which

-   -   at least one surface of the flat metal workpiece is anodically        poled in a treatment liquid and an anodic dissolving process is        thereby induced, and then    -   the at least one surface of the flat metal workpiece is        cathodically poled in the treatment liquid and a cathodic        deposition process is thereby induced for the deposition of one        or more metals on the at least one surface of the flat metal        workpiece,    -   characterized in that a conductive liquid based on sulphuric        acid/sulphate solutions of copper is used as treatment liquid        (electrolyte) and the treatment liquid further contains one or        more members selected from the group consisting of yttrium,        lanthanum and lanthanoids. The ratio between (i) the sum of the        amount-of-substance fractions (in mol/l) of yttrium, lanthanum        and/or the lanthanoids, where contained, and (ii) the        amount-of-substance fractions (in mol/l) of copper is 0.0182 or        more, preferably 0.0182 to 0.127.

The method according to the invention provides a simple and efficientmethod for increasing the adhesive strength of flat metal workpieces.

DETAILED DESCRIPTION OF THE INVENTION

The present invention provides a method for the electrolytic surfacemodification of a flat metal workpiece, in which at least one surface ofthe flat metal workpiece is anodically poled in a treatment liquid andan anodic dissolving process is thereby induced, and then the at leastone surface of the flat metal workpiece is cathodically poled in thetreatment liquid and a cathodic deposition process is thereby inducedfor the deposition of one or more metals on the at least one surface ofthe flat metal workpiece.

The treatment liquids used in the method according to the invention areconductive liquids based on sulphuric acid/sulphate solutions of copper.They are produced simply by dissolving suitable salts or oxides ofcopper in aqueous sulphuric acid. The quantity of sulphuric acid used ispreferably chosen such that a residual concentration of free sulphuricacid remains after the dissolving. This residual concentration of freesulphuric acid is preferably at least 0.664 mol/l.

The molar ratio (i.e. the ratio of the amount-of-substance fractions)between copper ions and free sulphuric acid is preferably in the rangeof from 1.05 to 1.25, more preferably 1.10 to 1.20, in particular in therange of from 1.15 to 1.17. In a specific embodiment, the ratio isapproximately 1.16. Among other things, copper(II) sulphatepentahydrate, copper(II) oxide, copper(II) carbonate or basic copper(II)carbonate are suitable as copper source.

Furthermore, one or more conducting salts are added to the treatmentliquid. In the case of the present invention, salts of the rare earthelements (REE) yttrium, lanthanum and the lanthanoids (Ln), whichconvert into readily soluble sulphatometallates of the general formulaCu₃[REE(SO₄)₃]₂ (REE=rare earth elements) in the acidic treatment liquidare suitable as conducting salts. The element(III) oxides and theelement(III) carbonates are suitable, among other things, as source foryttrium, lanthanum and the lanthanoids. Lanthanum oxide is particularlypreferred. The yttrium, lanthanum or lanthanoid salts are added to thetreatment liquid in a quantity such that the molar ratio between (i) thesum of the amount-of-substance fractions of Y, La and/or Ln, wherecontained, and (ii) the amount-of-substance fractions of copper is0.0182 or more, preferably 0.0182 to 0.127. The concentration of the sumof yttrium, lanthanum or lanthanoid ions is preferably 0.014 mol/l ormore, it is preferably in the range of from 0.014 mol/l to 0.35 mol/l,and in particular in the range of from 0.024 to 0.098 mol/l.

In particular, in the case of high ratios between yttrium, lanthanumand/or lanthanoids and copper (>0.024), the sequence of solution of thecomponents is decisive for the rapid preparation of the electrolyte:first of all, the aqueous sulphuric acid is put in, then the copper(II)compound is dissolved and optionally insoluble constituents areseparated off in the case that oxides/carbonates of the copper are used.Then, the compound(s) of Y, La and/or Ln used are dissolved. Thecarbonates and the lanthanum oxides/lanthanoid oxides must always beadded with thorough stirring and in partial portions appropriate to thebatch size in order to rule out excessive foaming or spattering of theforming electrolyte solution through the carbon dioxide released orotherwise occurring local overheating [La(III) and Ln(III) oxides reacthighly exothermically with acids].

Examples of suitable acidic treatment liquids (electrolytes) based oncopper sulphate are shown in the following Table 1.

TABLE 1 Aqueous sulphuric acid copper REE electrolytes which wereproduced from the corresponding oxides of the conductive ions (LaO, YO,NdO, GdO or DyO). Conc., free Conc. Counterions for Conductive Conc. Cuions sulphuric acid conductive Cu and Electrolyte name ion in mol/l inmol/l ions in mol/l conductive ions Electrolyte 1 La 0.77 0.664 0.0245Sulphate Electrolyte 2 La 0.77 0.664 0.0490 Sulphate Electrolyte 3 La0.77 0.664 0.098 Sulphate Electrolyte 4 Y 0.77 0.664 0.0245 SulphateElectrolyte 5 Nd 0.77 0.664 0.0245 Sulphate Electrolyte 6 Gd 0.77 0.6640.0245 Sulphate Electrolyte 7 Dy 0.77 0.664 0.0245 Sulphate

The addition of yttrium, lanthanum and/or lanthanoid ions to thetreatment liquid in the method according to the invention for surfacemodification results not in the typical columnar aggregates (also called“dendrites” below) being deposited on the surface to be modified of theflat metal workpiece but rather balls covered with vertical lamellae.The adhesive bond (adhesive force per unit of area) of these aggregatescompared with for example plastic increases depending on the specificratios to twice to almost three times the adhesive bond of theconventionally produced treatment.

The incorporation of the rare earth elements (Y, La and/or Ln) added asconducting salts into the copper layer was found as an additional effectin the deposition from the acidic copper(II) REE sulphate treatmentliquids. While the diamagnetic REE(III) ions of the yttrium and thelanthanum are incorporated only loosely bound, the paramagnetic Ln(III)ions of neodymium, gadolinium or dysprosium for example are incorporatedfirmly anchored into the copper layer at the same concentration in thetreatment liquid. This is shown in Table 2.

TABLE 2 Incorporation of rare earth elements (REE) from acidiccopper(II) REE sulphate treatment liquids in the copper layer depositedon the surface of the flat metal workpiece Conc. in the Effectivetreatment magnetic moment Molar ratio in the REE(III) ion liquid (mol/l)REE(III) (μb) layer n(REE)/n(Cu) Yttrium 0.0246 0 0.0036 Lanthanum0.0246 0 0.0006 Lanthanum 0.0492 0 0.0013 Neodymium 0.0246 3.6 0.0058Gadolinium 0.0246 7.8 0.0024 Dysprosium 0.0246 10.8 0.0021

The structuring of the deposited layer and the incorporation of the REEmetals in the copper layer not only depend in a causal way on themagnetic properties of the REE(III) ions but the solubility gradient ofthe sulphatometallates Cu₃[REE(SO₄)₃]₂ has a significant influence inthe transition from the comparatively readily soluble copper salts tothe less soluble acids H₃[REE(SO₄)₃] (cathodic process). Since thesolubility of the sulphates increases significantly after neodymium, theeffect of the heavy REE ions on the deposition process decreases. Thisdecisive equilibrium for the deposition of the structured copper layerforces high mass transfer in the area of the electrolytic processes inorder, in particular in the case of large molar REE-Cu ratios, to beable to rule out stationary, macroscopic precipitations of REE(III)sulphates (salt spots).

Moreover, the treatment liquid can contain further control additives andadditives which influence the viscosity, thermal conductivity,electrical conductivity and/or the deposition of the metal aggregates.For example, the treatment liquid can comprise an additive of thegeneral formula (I):

HO—CHR⁸—CHR⁹—Z—(CHR⁴—CHR⁵—Z)_(n)—CHR⁶—CHR⁷—OH  (I)

in which:

-   -   n=an integer from 1 to 11, in particular an integer from 1 to 3,    -   Z═S or O, in particular S,    -   R⁴═H, C₁₋₄-alkyl or phenyl,    -   R⁵═H, C₁₋₄-alkyl or phenyl,    -   R⁶═H, C₁₋₄-alkyl or phenyl,    -   R⁷═H, C₁₋₄-alkyl or phenyl,    -   R⁸═H, C₁₋₄-alkyl or phenyl, and    -   R⁹═H, C₁₋₄-alkyl or phenyl.

When the compound of formula (I) comprises enantiomers or diastereomers,both pure enantiomers or diastereomers and corresponding mixtures can beused.

In particular, within the framework of the present invention, C₁₋₄-alkylis methyl, ethyl, n-propyl, iso-propyl, n-butyl, iso-butyl or sec-butyl,preferably methyl, ethyl, n-propyl, or n-butyl.

Preferably in the case of the additive of formula (I):

-   -   n=an integer from 1 to 3,    -   Z═S,    -   R⁴═H, methyl, ethyl, n-propyl, or n-butyl,    -   R⁵═H, methyl, ethyl, n-propyl, or n-butyl,    -   R⁶═H, methyl, ethyl, n-propyl, or n-butyl,    -   R⁷═H, methyl, ethyl, n-propyl, or n-butyl,    -   R⁸═H, methyl, ethyl, n-propyl, or n-butyl, and    -   R⁹═H, methyl, ethyl, n-propyl, or n-butyl.

Alternatively, the additive of formula (I) is a compound of formula(II):

HO—(CHR⁶—CHR⁷—Z)_(n)—CHR⁶—CHR⁷—OH  (II)

in which:

-   -   n=an integer from 1 to 11,    -   Z═S or O,    -   R⁶═H, methyl or phenyl, and    -   R⁷═H, methyl or phenyl,        wherein preferably n=1-3 and Z═S.

Particularly preferably, the additive is a compound of formula (I), inwhich:

-   -   n=1 or 2, in particular 1,    -   Z═S,    -   R⁴═R⁵═H or methyl,    -   R⁶═R⁹═H or methyl, and    -   R⁷═R⁸═H or methyl.

Even more preferably, the additive is a compound of formula (III):

HO—CHR⁸—CHR⁹—S—CH₂—CH₂—S—CHR⁶—CHR⁷—OH  (III)

in which

-   -   R⁶═R⁹═H or methyl, and    -   R⁷═R⁵═H or methyl.

A particularly preferred additive of the general formula (I) which canbe used in the treatment liquid in the method according to the inventionis 1,8-dihydroxy-3,6-dithiaoctane (DTO).

The additives of formula (I) are commercially available or can beobtained through known chemical synthesis methods or analogously to thelatter.

In addition, the following additives can be used to influence thesurface tension and the dissolution rate of the finest gas bubbles:

Surface-active substances of the general formula:

C_(n)H_(2n+1)(OC₂H₄)_(x)—O—(H,C_(m)H_(2m+1)) with n=8 to 18, and x=3 to9, m=1 to 4

C_(n)H_(2n+1)(OC₃H₆)_(y)—OH with n=8 to 16 and y=1 to 3.

C_(n)H_(2n+1)(OC₂H₄)_(v)—(OC₃H₆)_(w)—OH with n=10 to 16 and v=4 to 5,w=2 to 4, from w=½v to w+1=v

The possible surface-active substances are added individually or as amixture, wherein the total concentration in the electrolyte must alwayslie below the saturation limit, as a rule below 0.05 wt.-%. The use ofthe terminally-etherified polyethoxylates which are less sensitive tooxidation on the anode is advantageous.

In an embodiment of the invention, the method according to the inventionis carried out according to the neutral conductor principle, i.e. theflat metal workpiece is contacted neither cathodically nor anodicallybut is polarized anodically (positively) by at least one cathode and isthen polarized cathodically (negatively) by at least one anode. Thecurrent is transferred to the flat metal workpiece not by directcontacting of the flat metal workpiece via a contact element (e.g. acurrent roll) connected to a current source, but through the treatmentliquid. During the anodic polarization, an anodic dissolving or erosionprocess is induced on a surface of the flat metal workpiece in whichtiny particles and residues or impurities located on the surface of themetal foil are removed, whereby a clean surface is obtained.Furthermore, the topographical features of the metal surface, inparticular the roughness peaks, are leveled.

Furthermore, the anodic polarization or the anodic dissolving processinduced thereby leads to an activated surface for the subsequent metaldeposition. In particular, the surface obtained with the methodaccording to the invention exhibits structural similarity or structuralidentity with the metal aggregates deposited on the surface of the flatmetal workpiece in the subsequent deposition process (epitaxy orsyntaxy). Furthermore, because of the fact that the flat metal workpieceis completely covered by the treatment liquid during the entireelectrolytic treatment, it can largely be avoided that the definedactivation state of the surface is lost due to contact with thesurrounding atmosphere. Through the cathodic polarization which follows,a cathodic deposition process is induced, in which a metal or a metalalloy (i.e. several different metals) is deposited on the surface of theflat metal workpiece.

The flat metal workpiece used within the framework of the presentinvention is preferably a metal workpiece with a thickness which is atleast 100 times, preferably at least 1,000 times and particularlypreferably at least 10,000 times smaller than the length and/or width ofthe metal workpiece. Consequently, as a rule, the term “surface of theflat metal workpiece” means the area defined by the length and width,not the area defined by the thickness and width or thickness and length.The flat metal workpiece is preferably a metal strip or a metal foil.The term “metal strip” herein refers to a flat metal workpiece with agiven width and a thickness of from 100 μm to 1 mm. The term “metalfoil” refers to a flat metal workpiece with a given width and athickness of 100 μm or less, preferably with a thickness in the range offrom 10 μm to less than 100 μm.

As a rule, the flat metal workpiece consists entirely of a single metal,in particular of copper, tin, silver or iron. However, it can alsoconsist of a metal alloy, for example of at least two of the namedmetals, preferably of a copper wrought alloy, iron alloy, silver alloyand tin alloy. A flat metal workpiece made of steel can also be used.Particularly preferably, the flat metal workpiece is a copper foil, acopper strip, a silver foil, a silver strip, a tin-plated foil or atin-plated strip, in particular a tin-plated copper foil or a tin-platedcopper strip.

Furthermore, the flat metal workpiece can also consist of two or morelayers of a metal or a metal alloy, wherein the layers can be the sameor different. Furthermore, the flat metal workpiece can be formed insuch a way that at least one and preferably both surfaces of the flatmetal workpiece consist of a metal or a metal alloy and the remainingpart of the flat metal workpiece can be made of any material, as long asthis is suitable for use in the method according to the invention.

Before use in the method according to the invention, the flat metalworkpiece is usually pre-treated. Appropriate pre-treatment methods areknown in the state of the art and comprise, for example, degreasing,rinsing with water, aqueous surfactant solutions or solvents, andpickling with sulphuric acid.

During the electrolysis, the flat metal workpiece is preferably guidedthrough the treatment liquid and past the at least one cathode and theat least one anode. This is carried out in such a way that the describedanodic polarization and cathodic polarization and the anodic dissolvingprocess and cathodic deposition process thereby induced take place. Inthe case of continuous metal foils or strips, these are usually guidedthrough the treatment liquid using guiding elements (e.g. guiderollers). If a continuous foil installation is used to carry out themethod according to the invention, several electrolysis baths(electrolytic cells) can also be connected in series.

Within the framework of the present invention, a variety of arrangementsof the at least one cathode and the at least one anode are conceivable.For example, 1, 2, 3, 4 or more cathodes and 1, 2, 3, 4 or more anodescan be used per electrolytic cell or electrolyte bath. These can bearranged differently (e.g. alternately cathode and anode, first allcathodes and then all anodes, several cathodes alternating with severalanodes, cathodes and anodes arranged only on one side of the flat metalworkpiece or on both sides, etc.).

According to a preferred embodiment, at least one cathode pair and atleast one anode pair are preferably used. The two cathodes of thecathode pair and the two anodes of the anode pair are arranged onopposite sides of the flat metal workpiece such that the flat metalworkpiece is located between the two anodes and between the twocathodes. Anodic or cathodic polarization consequently occurs on bothsides of the flat metal workpiece. Such a configuration permits thetwo-sided modification of the flat metal workpiece with deposited metalaggregates. According to another preferred embodiment, the flat metalworkpiece is first of all anodically polarized by two cathodes which arearranged on the same side of the flat metal workpiece and thencathodically polarized by two anodes which are both arranged on the sameside of the flat metal workpiece as the cathodes. A separate rectifieris necessary for each side of the substrate (electrode pair).

Usually, the at least one surface of the flat metal workpiece is firstanodically polarized by the at least one cathode and then cathodicallypolarized by the at least one anode. However, it is also provided thatthe cycle “anodic polarization/cathodic polarization” is run throughseveral times. Furthermore, the flat metal workpiece can be polarizedone or more times anodically and one or more times cathodically in anysequence, wherein typically the anodic dissolving process predominatesfirst and then the cathodic deposition process predominates. A phasewith a dominating dissolving process can be interrupted by a short phasewith the deposition process (dominating dissolving process, interruptedby deposition process) and vice versa (dominating deposition process,interrupted by dissolving process). The one or more anodic polarizationsand the one or more cathodic polarizations can, as already mentionedabove, be achieved using a corresponding number of spatially separatedanodes and cathodes. However, it is also possible to use electrodeswhich are connected (contacted) optionally positively or negatively andconsequently function both as cathode and as anode.

The cathodes and anodes are operated with direct current or a pulsedcurrent, usually a pulsed direct current. Rectifiers can be used forthis. If the number of electrodes exceeds two (i.e. more than onecathode and/or more than one anode), the additional electrodes arepreferably operated through an additional rectifier. Within theframework of the present invention it is also possible for eachelectrode to be supplied by another rectifier in at least one operatingregion (cathodic, anodic), while in another operating region severalrectifiers can be connected to one electrode.

Insoluble or soluble anodes can be used as anodes in the methodaccording to the invention. The insoluble anodes typically consist of aninert material (or oxides thereof), such as, for example, lead,graphite, titanium, platinum and/or iridium (and/or oxides thereof).Preferred insoluble anodes are made of titanium coated with platinum oriridium and/or ruthenium (and/or oxides thereof). A titanium anodecoated with iridium or iridium oxide is particularly preferred. On theother hand, the soluble anodes consist of the metal to be coated or themetal alloys to be coated. Examples of suitable soluble anodes areanodes made of copper or tin.

Suitable cathodes can consist of the same material as the material ofthe anodes. A copper cathode can be used, for example, as cathode. In apreferred embodiment, copper electrodes are used both as anode and ascathode.

The working temperature of the treatment liquid, also called electrolytein the following, is preferably between 10° C. and 60° C., particularlypreferably between 20° C. and 50° C. In order to keep the treatmentliquid in this temperature range, it can be continuously cooled orheated.

The necessary recirculation of the treatment liquid depends on thecurrent density used in the electrolytic deposition. The recirculationis necessary in order to reduce to a sufficient minimum the thickness ofthe electric double layer. The recirculation in the electrode chambercan be ensured, for example, by installing one or more pumps. Therecirculation serves above all to preserve the functional efficiency ofthe electrodes and to avoid salt spots on the foil to be treated. Thestacking effects occurring already in the currentless state through thesulphatometallates lead to an extreme primary voltage in order even toset the electrolytic process in motion. This primary voltage can bereduced so much by targeted increase in the recirculation at theelectrode surfaces and at the material to be treated in conjunction witha well-chosen time gradient of the current density increase that theseelectrolytes are available for technical use. The necessaryrecirculation and the current density gradient depend directly on theREE/Cu ratio used and on the actual REE ion in the sulphate electrolyte.Lanthanum(III) ions provide the greatest sensitivity and thus the bestpossible process adjustment.

The following data for the recirculation given in Table 3 relate to anelectrolyte volume in the treatment chamber of 50 litres, anelectrode-foil distance of 20-30 mm and a width and height of thepolarization chamber of 240 mm (H) and 300 mm (W). In addition to thetargeted recirculation, the circulation delivers 1.2 l/min. over thefiltration bypass.

TABLE 3 Dependency of the recirculation and of the current densitygradient on the La/Cu weight ratio and on the current density gradientCurrent Current density Recircu- density in the La—Cu lation gradient A/Pulse process Electrolyte wt. ratio in l/min. dm²s form^(b)) A/dm²Electrolyte 1 0.032  1.2 0.66 10001 3.3 Electrolyte 1 0.032 40a) 2.2510997 22.5 Electrolyte 2 0.064 40 1.13 10997 22.5 Electrolyte 3 0.127 400.38 10997 22.5 ^(a))40 l/min. corresponds to a flow on the surfaces ofthe electrode chamber of approx. 2.65 l/(min * dm²) ^(b))the pulseforms/rates 10001 = 50 mS 1, 50 mS = 0; leff = ½ l(1) 10997 = 50 ms 1,50 ms 5, 50 ms 1, 50 ms 7 = 1 cycle; leff = 3.5 l(1)

Preferably at least one cathode and/or at least one anode of the deviceis designed as flow electrode which comprises an electrode housing witha metal mesh through which the treatment liquid can enter the housing.The electrode housing is at least partially filled with metal ballswhich are in contact with each other and with the metal mesh. Theelectrode housing further comprises an electrolyte feed for introducingan electrolyte and a flow opening out of which the electrolyte which hasflowed through from the electrolyte feed between the metal balls to theflow opening exits. The flow opening is arranged such that a sufficientflow takes place through the operating zone, i.e. the space betweenelectrode and flat metal workpiece. For this, the flow opening isusually arranged so that the exiting electrolyte flows past the metalmesh. The flowing past preferably takes place substantially parallel tothe metal mesh.

The flat metal workpiece treated with the method according to theinvention is usually subjected to an after-treatment. Suchafter-treatment methods are known in the state of the art and comprise,for example, rinsing with water or solvents, passivation, for examplewith a chromium(VI)-containing solution, and drying.

As an example of a device for carrying out the method according to theinvention, a device is named which comprises at least one container forreceiving a treatment liquid, at least one cathode arranged in thecontainer and at least one anode arranged in the container, wherein theat least one cathode and the at least one anode are connected to acurrent source and wherein the flat metal workpiece is not connected toa current source.

In addition, the electrode housing usually comprises a cover, in orderto prevent the metal balls from falling out and to ensure a defined flowof electrolyte through the flow electrode. The cover can be connecteddetachably, for example with knurled screws, to the electrode housingand furthermore comprise contacts for connecting to a current source.During operation, the flow electrode is connected anodically orcathodically to a current source, wherein the metal mesh is usuallycontacted anodically or cathodically.

The electrolyte which has flowed through the metal balls is preferablycollected in an electrolyte channel and then supplied to the flowopening. The electrolyte channel and the flow opening are preferablylocated in the base of the electrode housing. The flow opening ispreferably designed as a flow lip which preferably extends over theentire length of the metal mesh in the base of the electrode housing. Ifa filter nonwoven arranged in front of the metal mesh is used as anodebag, the flow opening is arranged such that the electrolyte exits infront of the filter nonwoven and flows along the latter substantiallylaminar.

The electrode housing can, for example, consist of a plastic, such aspolypropylene. The metal balls can consist of the metals named above forthe anode and cathode. Preferably, at least one anode is designed in theform of the flow electrode described above. In the case of the anode,the metal balls preferably consist of the metal or the metals which areto be deposited on the flat metal workpiece. The metal balls arepreferably copper balls. The metal mesh is preferably an expanded metalmesh (expanded metal screen area), in particular a titanium expandedmetal.

FIG. 1 shows schematically an embodiment of a dissolving/deposition cell30 for carrying out the method according to the invention for surfacetreatment of a flat metal workpiece 32, in this case a metal foil. Thedissolving/deposition cell 30 has a trough-like container 31, open atthe top, in which a treatment liquid 36 is located. Thedissolving/deposition cell 30 further has a first, second and thirdguide roller 34 a, 34 b and 34 c and a first working electrode, whichconsists of two cathodes 40 a and 40 b arranged parallel, and a secondworking electrode, which consists of two anodes 44 a and 44 b arrangedparallel. The cathodes 40 a and 40 b and the anodes 44 a and 44 b areconnected to a current source 45. The first and third guide rollers 34a, 34 c are arranged above the container 31 outside the treatment liquid36 and above the first and second working electrodes, while the secondguide roller is located on the base of the container 31 within thetreatment liquid and below the working electrodes. Furthermore, thedissolving/deposition cell 30 has a separating element 48 for reducingblind currents.

The flat metal workpiece 32 runs into the treatment liquid 36 via thefirst guide roller 34 a and through between the two cathodes 40 a, 40 b,with the result that the latter are located in each case on one of thetwo sides of the flat metal workpiece 32 passing through. Neither theflat metal workpiece 32 nor the first guide roller 34 a is connected toa current source. The region 38 a of the flat metal workpiece 32 locatedbetween the two cathodes 40 a, 40 b is positively (anodically) polarizedby the two cathodes 40 a, 40 b. The two cathodes 40 a, 40 b define adissolving region 42. In the enlarged and schematically representedsection of the dissolving region 42, impurities and possibly occurringforeign metals and/or particular (e.g. uneven) metal structures presenton the surface of the flat metal workpiece 32 are largely eliminated. Asa result, an impurity-free, homogeneous and defined surface of the flatmetal workpiece 32 is obtained which is suitable for achieving definedmetal structures in the subsequent deposition step.

After passing through the cathodes 40 a, 40 b, i.e. the dissolvingregion 42, the flat metal workpiece 32 is guided via the second guideroller 34 b, which likewise is not connected to a current source,between the two anodes 44 a, 44 b, which are located in each case on oneof the two sides of the flat metal workpiece 32 and form the secondworking electrode. A region 38 b of the flat metal workpiece 32 ispolarized negatively (cathodically) by the two anodes 44 a, 44 b. Thetwo anodes define a deposition region 46. In the enlarged andschematically represented section of the deposition region 46, thepositively charged metal ions of the treatment liquid 36 migrate to thenegatively polarized surface of the flat metal workpiece 32 and aredeposited in a defined manner on the surface of the flat metal workpiece32. After passing through the deposition region 46, the flat metalworkpiece 32 runs out of the treatment liquid 36 and over the thirdguide roller 34 c which is not connected to a current source.

A further subject-matter of the present invention is a flat metalworkpiece which was produced with the method according to the invention.It was surprisingly found that the method according to the inventionleads to the formation of metal aggregates on the surface of the flatmetal workpiece, wherein these metal aggregates have the shape of ballscovered with vertical lamellae. They differ thereby from the columnardendrites as are obtained with the usual methods of the state of theart.

FIG. 2 shows a dark field picture (Nikon Eclipse ME600 reflected-lightmicroscope with dark-field unit, camera Leica DFC290, lenses 100×; 50×;20×; 10×; 5×; software Leica Application Suite 2.6.0 R1; magnification500 times) of a copper foil surface which was modified according to themethod of the invention by deposition of La/Cu from sulphuric acidelectrolyte with an La concentration of 14.0 g/l, a Cu concentration of50.3 g/l and an [La]:[Cu] weight ratio of 0.127 (electrolyte 3) in thecontinuous foil installation described below. At this magnification, thespherical metal aggregates on the copper foil surface are clearlyrecognizable.

FIG. 3 shows an SEM photograph of a copper foil surface treatedelectrolytically according to the method according to the invention withsulphuric acid neodymium-copper electrolyte with an Nd:Cu weight ratioof 0.032 at a magnification of 10,000 times. The photograph reproduces asection of a spherical metal aggregate on the copper foil surface andmakes the lamella structure thereof visible.

FIG. 4 shows a dark field picture (Nikon Eclipse ME600 reflected-lightmicroscope with dark-field unit, camera Leica DFC290, lenses 100×; 50×;20×; 10×; 5×; software Leica Application Suite 2.6.0 R1; magnification500 times) of a copper foil surface which was modified according to themethod of the invention but by deposition of Cu from sulphuric acidelectrolyte with a Cu concentration of 7.0 g/l (electrolyte) in thecontinuous foil installation described below. At this magnification, thecolumnar metal aggregates on the copper foil surface are clearlyrecognizable.

The roughness of the metal surface increases to a small extent throughthe deposition of the metal aggregates. For example, after thedeposition of the metal aggregates on a copper foil, the averageroughness values Ra and Rz, determined in accordance with DIN EN ISO4288:1998, are preferably in the range of from 0.22 to 0.32 μm and inparticular in the range of from 0.24 to 0.28 μm for Ra, and preferablyin the range of from 1.4 to 2.1 μm and in particular in the range offrom 1.6 to 1.9 μm for Rz. In contrast, before the deposition, a copperfoil has, for example, roughness values of approximately 0.20 μm for Raand 1.3 μm for Rz.

It was surprisingly established that the adhesive strength of the metalsurface which is obtained through the deposition of aggregates in theform of balls covered with vertical lamellae on a surface of a flatmetal workpiece according to the method according to the invention issurprisingly high. The adhesive strength, determined in accordance withthe 180° peel test described below using an FR-4 epoxy resin andexpressed as peel strength in N/mm, preferably lies at or over 1.5 N/mm.In the case of a copper foil or a copper strip, the peel strengths arepreferably 1.5 to 3.0 N/mm, in particular 1.8 to 3.0 N/mm.

Because of their excellent adhesive strength, the flat metal workpiecesaccording to the invention can be used as substrate for the formation ofstrong adhesive bonds with a plurality of materials. In particular, themetal aggregates on the surface of the flat metal workpiece lead to astrong adhesive bond on pressing or rolling (roll cladding) with thesame or another material, on lacquering with or without subsequentcuring/crosslinking or on gluing. A plurality of materials come intoconsideration as adhesion partner for the metal workpiece according tothe invention, for example thermoplastics such as PA 66, PI and PET,synthetic resins (epoxides), adhesives, lacquers and pastes, such asgraphite pastes.

The present invention therefore also relates to the use of the metalworkpieces produced according to the method according to the inventionas substrate for the formation of strong adhesive bonds. The flat metalworkpieces according to the invention can be used for a plurality ofapplications. Laminates of copper with PET for the shielding of cablesand plug and appliance housings from electromagnetic interferences, inparticular in signal transmission, can be named by way of example.Furthermore, the use as electrical conductor in the production of MID(moulded interconnect devices) circuits is to be mentioned. These arecircuits which are based on hot stamping of metallic foils onthermoplastic substrates. A further application is as substrate forelectrode material in battery technology. In particular, the flat metalworkpieces according to the invention can also be used in the productionof stable connections required in circuit-board technology for theproduction of copper laminates. Specifically in the production ofcircuit boards, the adhesive strength of the metallic conductor on thesubstrate (e.g. FR-4) is of central importance. This is due on the onehand to the process steps necessary in the production (etching,drilling, pressing) and on the other hand to the load on the circuitboard in the end product itself.

EXAMPLES Materials

Various sulphuric acid sulphate electrolytes of copper with or withoutthe addition of lanthanum conducting salt were used as electrolytes foruse in the following examples. The composition of these electrolytes isshown in Table 4.

TABLE 4 Properties and composition of the electrolytes used in theexamples Electrolyte 0^(a)) Electrolyte 1 Electrolyte 2 Electrolyte 3Density 1.07 1.19 ± 0.02 1.21 ± 0.02 1.24 ± 0.02 (g/cm³) pH value^(b))1.9 ± 0.3 1.9 ± 0.3 1.9 ± 0.3 1.9 ± 0.3 Copper 7.0 48.9 49.5 50.3content (g/l) Lanthanum 0 3.41 6.9 14.0 content (g/l) Sulphate 69.4 77.580.7 94.2 content (g/l) Sulphuric 60.0 61.5 62.3 63.3 acid (g/l)[La]:[Cu] 0 0.032 0.064 0.127 (wt./wt.) ^(a))Electrolyte 0: forcomparison ^(b))pH value determined for a concentration of theelectrolyte of 10 g/l All La—Cu electrolytes (Electrolyte 1, 2 and 3)contain traces of in total less than 0.2 g/l heavy lanthanoids, such aspraseodymium, neodymium and samarium.

Electrolysis Devices

In the examples described herein, on the one hand a continuous foilinstallation was used and on the other hand a static electrolysisarrangement.

Continuous Foil Installation

The continuous foil installation used is designed for foils and stripsup to a width of 330 mm. The machine has a pay-off reel and a pay-onreel with electronic tension control. The control possibilities comprisecurrent strength of the individual electrode segments, strip tension,strip speed and temperature of the electrolyte. The rectifiers usedoriginate from the company plating electronic, pe86CW-6-424-960-4 typewith 4 outputs. The maximum pulse current is 960 A, the maximum constantcurrent is 424 A. The course of the current with respect to time can bedefined as the pulse sequence via the associated software.

The electrolytic cell of the continuous foil installation used comprisesa cathode and an anode for one-sided electrolytic deposition. Thecathode and the anode are positioned parallel to the foil run andarranged such that, when the foil passes through, the same side orsurface of the metal foil is opposite first the cathode and then theanode. Furthermore, the cathode and the anode are completely surroundedby electrolyte. Although in the tests described herein only one cathodeand one anode is used, a plurality of different configurations can beused, for example a double cathode and a double anode for electrolyticdeposition on both sides or two cathodes and anodes arranged one afterthe other.

In the tests described in the following, either a three-part convectionelectrode or a flow electrode are used as electrodes (anode andcathode). These are connected to rectifiers (pe86CW-6-424-960-4 typewith 4 outputs from the company plating electronic, maximum pulsecurrent 960 A, maximum constant current 424 A). The course of thecurrent with respect to time can be defined as the pulse sequence viaappropriate software. Furthermore, the current strengths of theindividual electrodes, the strip speed and tension as well as theelectrolyte temperature are controllable.

The three-part convection electrode used has three electrode segmentsconsisting of a copper sheet. Although the individual electrode segmentscan be controlled separately via a rectifier, in the following tests allof the electrode segments were connected with the same polarity. Theelectrode is located in an anode bag made of polypropylene fabric. Thenecessary flow is produced by means of a B2 rod pump from Lutz (in total40 l/min. distributed over 2 electrodes).

The flow electrode used comprises an electrode housing made ofpolypropylene and a high-current titanium contact frame with a screensurface made of titanium expanded metal which is packed behind withcopper balls. The electrode is located in an anode bag made of PPfabric. The possible flow rate is up to 20 l/min. The electrolyte isintroduced into the flow electrode via an electrolyte feed, flows pastthe metal balls in the direction of the base of the housing of theelectrode housing and is received by an electrolyte channel in the baseof the electrode housing. The electrolyte then exits the electrolytechannel via a flow opening in the form of a flow lip and flows upwardspast the metal mesh. In the continuous foil installation used, afterpassing through the flow electrode, the electrolyte reaches theelectrolysis bath and from there via an overflow a reservoir, from whichthe electrolyte is then pumped again into the flow electrode.

The flow electrode described above and used in the following examplesrepresents only one example of a flow electrode which can be usedaccording to the invention. It is clear to a person skilled in the artthat numerous embodiments, modifications and/or amendments areconceivable.

Static Electrolysis Arrangement

This electrolysis arrangement was used in order to simulate the changein polarization of the same surface of the flat metal workpiece usinglittle material which is typical for the method according to theinvention.

The static electrolytic cell comprises a 1,000 ml glass beaker filledwith an electrolyte (900 ml). The glass beaker stands on a heatedstirrer. The heated stirrer is used to heat the electrolyte, wherein thetemperature is constantly checked by a thermal element with a stainlesssteel sheath and is kept constant to within +/−2° C. The stirring speedis kept at 1,000 rpm and the stirring is transferred to the electrolytesolution by a round magnetic stir bar (PTFE) with dimensions of 40×d6.

Over the glass beaker there is a cover plate of PP, which is laid overthe glass beaker and has an electrode on both sides at a distance ineach case of 30 mm. These electrodes can consist of an inert material orbe made of the material of the foil to be treated. Exchange is possiblewithin a few minutes without problems. These electrodes are flat sheetswhich are immersed parallel to each other and in each caseperpendicularly into the electrolyte solution. The one-side, immersedsurface area is between 60 mm×80 mm and 60 mm×100 mm per electrode. Inthe centre, the plastic plate was provided with an opening of 20 mm×80mm parallel to the inert electrodes, through which opening the flexiblefoil holder can be introduced into the cell. This foil holder wastherefore formed flexible so that the foil, once inserted, can then passthrough the entire process, including the pre-treatment andafter-treatment steps (e.g. cleaning/rinse/rinse,etching/pickling/rinse/rinse, electrolysis/rinse/rinse,passivation/rinse/DI rinse) in the same holder and only needs to betaken out of the holder after the last rinse for drying. The foil holderconsists of two PP frames with a window of 80 mm×60 mm, into which thefoil is clamped. The clamping screws are manufactured from PA6 plastic.The lower clamping screws serve only to clamp the foil, the upperclamping screws serve in addition to produce a releasable press contactwith a TiPt expanded metal mesh. This contact point is immersed in thesolution, with the result that the foil is completely immersed in theelectrolyte and the contact point is blanked off from the field of thecell by the frame of the foil holder. The expanded metal used for thecontacting projects upwards out of the cell and is supplied with currentvia a crocodile clip. For the current supply, a power unit of theStatron type with pre-selectable current strength and display of thecorresponding voltage is used. A pole-inverter switch is located betweenthe power unit and the electrolytic cell, whereby the polarity of thefoil and of the electrodes can be reversed (switched) in any sequenceand at any time during the test.

Test Methods Test Method 1—Adhesion Test

An adhesive strip (Tesafilm® Transparent 57404-00002) was placed overthe electrolytically treated, dry, cold metal foil surface which hadbeen stored for at least 15 min. and pressed firmly onto the surfacewith a soft roller. Care was taken that no air bubbles formed betweenthe adhesive tape and the foil surface. After a period of 30 secondsafter the adhesive strip had been pressed on, it was gripped at itsprojection and pulled off from the firmly held metal foil. A pullingspeed of 2 to 3 seconds for a length of 8 cm was maintained.

The pulled off adhesive strip was then stuck to a white sheet of paperand the colour change caused by metal aggregates which are torn off fromthe foil surface and remain on the adhesive strip was assessed.Furthermore, it was assessed whether the adhesive layer of the Tesafilmremained either totally or partially on the surface of the metal foilafter the pulling off.

Test Method 2—Peel Strength Test

The peel strength was determined in accordance with DIN EN 60249 on aZwick BZ2/TN1S model peel device with an Xforce HP 500 N load cell andtestXpert 12.3 software. For this, the samples were cut out of a pressedcomposite sheet and the foil was pulled off or peeled off at an angle of180°. The pressed composite sheet was produced by pressing the foil witha plastic substrate at a temperature of 160±10° C. under a pressingpressure of 120±5 bar over a period of 60±5 min. The results of the peeltest are given in N/mm.

Example 1 Copper Deposition on Copper Foil by Means of a Continuous FoilInstallation Using Different Sulphuric Acid Copper Electrolytes with orwithout Addition of La Conducting Salt

A copper foil with a thickness of 0.035 mm and a width of 300 mm in thehard-as-rolled structural state was first subjected to a pre-treatmentwhich comprised the following steps in the stated sequence:

-   -   Degreasing: Immersion pass with electrolytic support, 45° C.,        alkaline cleaning agent    -   Rinse: Water, immersion pass, 45° C.    -   Pickling: Sulphuric acid 4% in water, immersion pass, 30-35° C.    -   Rinse: Water, immersion pass, room temperature    -   Rinse: Water, immersion pass, room temperature

The copper foil pre-treated in this way was then surface-modified in thedescribed continuous foil installation using the electrolytes of Table 4(Electrolyte 0, Electrolyte 1, Electrolyte 2, Electrolyte 3) and withthe following method parameters:

Strip speed: 1 m/min.,

Average current strength: 100 A,

Pulse sequence: 10 ms at 200 A, 10 ms rest,

Electrolyte temperature: 50±2° C.,

Recirculation by means of rod pump at 40 l/min.

After passing through the electrolysis apparatus, the surface-modifiedcopper foil was subjected to an after-treatment which comprised thefollowing steps in the stated sequence:

-   -   Rinse: Water, immersion pass, room temperature    -   Rinse: Water, immersion pass, room temperature    -   Passivation: Chromium(VI)-containing solution, immersion pass,        room temperature    -   Rinse: Water, immersion pass, room temperature    -   Rinse: De-ionized water, misting, room temperature    -   Drying with hot air 90° C.

The surface-modified foils obtained with Electrolytes 1, 2 and 3exhibited a uniform distribution of deposited spherical copperaggregates on the foil surface. FIG. 2 shows this on the example of asurface obtained with Electrolyte 3. In FIG. 4, the surface withcolumnar buildups obtained with Electrolyte 0 is shown for comparison.

The foil surfaces with lamellae-covered spherical aggregates obtainedwith Electrolytes 1, 2 and 3, moreover, had excellent adhesive strengthsof adhesives in the adhesion test using Tesafilm. The adhesion betweenthe modified metal foil surface and the adhesive on the adhesive stripis so high that, on pulling the adhesive strip off, the bond betweenadhesive and plastic carrier breaks and the adhesive layer of theTesafilm remains on the foil surface. In contrast, in the case of themetal foil modified with Electrolyte 0 (Cu electrolyte without La) withcolumnar treatment, the debonding of the treatment is observed onpulling off the adhesive strip.

Excellent adhesive strengths between 1.7 and 2.8 N/mm were also obtainedin the peel test. The peel strengths determined correlated withincreasing surface density of the deposited metal aggregates. Theresults of the peel test are summarized in Table 5 below.

TABLE 5 Peel strengths of copper surfaces pressed with FR-4 (V = foilspeed, I = average current strength, J = current density, Q = chargedensity) Peel V I J Q strength Electrolyte (m/min.) (A) (A/dm²) (C/dm²)Pulse form (N/mm) Electrolyte 2.5 100 13.9 80 10997* 2.8 ± 0.2 2Electrolyte 1 150 20.8 300 10997* 2.8 ± 0.2 2 Electrolyte 1 100 13.9 20010997* 1.7 ± 0.2 2 Electrolyte 1 100 13.9 200 10001** 2.0 ± 0.2 2Electrolyte 2 190 26.4 190 10997* 2.0 ± 0.2 2 Electrolyte 1 100 13.9 20010997* 2.4 ± 0.2 3 Electrolyte 1 45 1.5 260 10001* 1.2 ± 0.2 0 *Pulseform 10997 means: Rest for 50 ms; current of strength A (namely 166 A,250 A, 166 A, 317 A or 166 A) for 50 ms; rest for 50 ms; and current ofstrength B (greater than A) (namely 233 A, 350 A, 233 A, 443 A or 233 A)for 50 ms (this gives an average current (based on 50 ms) of I = 100 A,150 A, 100 A, 190 A or 100 A). **Pulse form 10001 means: Current ofstrength C (here 200 A) for 50 ms; rest for 10 ms.

Example 2 Incorporation of Rare Earth Elements (REE) into the Aggregateson the Surface of Copper Foil Modified with REE-Cu Electrolytes

A copper foil with a thickness of 0.035 mm and a width of 300 mm in thehard-as-rolled structural state was first of all subjected to apre-treatment which comprised the following steps in the statedsequence:

-   -   Pre-cleaning: Purax 6029PUS, 40 g/l, 60° C., currentless, 10 s.    -   Rinse: Water    -   Precision cleaning: Velocit 1127M, 25 g/l, 60° C., currentless,        10 s.    -   Rinse: Water    -   Etching/pickling: Sulphuric acid (7% in water), 25° C.-35° C.    -   Rinse: Water

The copper foil pre-treated in this way was then surface-modified in thedescribed static electrolysis arrangement using Electrolyte 1 andElectrolyte 2 at room temperature with a charge density of 541 C/dm²:

After passing through the electrolysis apparatus, the surface-modifiedcopper foil was subjected to an after-treatment which comprised thefollowing steps in the stated sequence:

-   -   Rinse: Water    -   Passivation: Solution of 6 g potassium dichromate in water at        room temperature.    -   Rinse: Water    -   Drying with hot air between 90° C. and 120° C.

In the case of further experiments within the framework of this example,the lanthanum in the treatment electrolyte Electrolyte 1 was replaced byequimolar quantities of yttrium, neodymium, gadolinium or dysprosium andthe surface modification was repeated with otherwise identicalparameters.

The layers deposited using the different electrolytes were analysed bymeans of ICP-OES from nitric acid solution (Argon-Plasma; Perkin Elmer,Optima 3000DV, axial registration emission; as standards in each casethe concentrations of 0.1 mg/l, 1 mg/l and 10 mg/l of the respective REmetal were used). The results are shown in Table 6.

TABLE 6 Concentration of the inert ions found in the deposited layer,relative to the treated surface in μmol/m² (from acidic REE-Cuelectrolytes). Inert ion Concentration in the aggregates Lanthanum(Electrolyte 1) 0 Lanthanum (Electrolyte 2) 0 Yttrium 0 Neodymium 42.0Gadolinium 13.3 Dysprosium 13.5

This example shows that lanthanum and yttrium are not incorporated intothe deposited aggregates after the electrolytic surface modification ofa copper foil with La—Cu or Y—Cu electrolytes. In contrast, withneodymium, gadolinium and dysprosium, these were recovered asparamagnetic inert ions after the decomposition by nitric acid of thedeposited aggregates.

1-13. (canceled)
 14. A method for the electrolytic surface modificationof a flat metal workpiece, comprising; (a) anodically polarizing atleast one surface of the flat metal workpiece with a treatment liquid,whereby an anodic dissolving process is induced, and then (b)cathodically polarizing said at least one surface of the flat metalworkpiece with the treatment liquid, thereby inducing a cathodicdeposition for the deposition of one or more metals on the at least onesurface of the flat metal workpiece, wherein said treatment liquid iscomprised of a conductive liquid based on sulphuric acid/sulphatesolutions of copper and one or more members selected from the groupconsisting of yttrium, lanthanum and lanthanoids, wherein the ratiobetween (i) the sum of the amount-of-substance fractions of yttrium,lanthanum and/or the lanthanoids, where contained, and (ii) theamount-of-substance fraction of copper is at least 0.0182.
 15. Themethod according to claim 14 wherein the amount-of-substance fraction ofcopper is 0.0182 to 0.127.
 16. The method according to claim 14, whereinthe flat metal workpiece is anodically polarized by at least one cathodewithout direct contacting for the induction of the dissolving process,and the flat metal workpiece is cathodically polarized by at least oneanode without direct contacting for the induction of the depositionprocess, and the cathode and the anode are arranged in such a way thattreatment liquid is located between anode and metal workpiece andbetween cathode and metal workpiece.
 17. The method according to claim14, wherein the concentration of the sum of yttrium, lanthanum andlanthanoids, where present, in the treatment liquid is at least 0.01mol/l.
 18. The method according to claim 17 wherein the concentration ofthe sum of yttrium, lanthanum and lanthanoids, where present, in thetreatment liquid is in the range from 0.014 mol/l to 0.35 mol/l.
 19. Themethod according to claim 14 wherein the treatment liquid comprises aconductive liquid based on sulphuric acid/sulphate solutions of copperand lanthanum.
 20. The method according to claim 14 wherein thelanthanum is present as lanthanum oxide
 21. The method according toclaim 14, wherein the treatment liquid additionally comprises anadditive of the general formula (I):HO—CHR⁸—CHR⁹—Z—(CHR⁴—CHR⁵—Z)_(n)—CHR⁶—CHR⁷—OH  (I) in which: n=aninteger from 1 to 11, Z═S or O, R⁴═H, C₁₋₄-alkyl or phenyl, R⁵═H,C₁₋₄-alkyl or phenyl, R⁶═H, C₁₋₄-alkyl or phenyl, R⁷═H, C₁₋₄-alkyl orphenyl, R⁸═H, C₁₋₄-alkyl or phenyl, and R⁹═H, C₁₋₄-alkyl or phenyl. 22.The method according to claim 21, wherein the additive is1,8-dihydroxy-3,6-dithiaoctane.
 23. The method according to claim 14,wherein a metal strip or a metal foil is used as flat metal workpiece.24. A flat metal workpiece upon which is deposited on the surfacethereof metal aggregates in the form of balls covered with verticallamellae, said surface having average roughness values Ra and Rz values,as determined in accordance with DIN EN ISO 4288:1998, ranging from 0.22to 0.32 μm and 1.4 to 2.1 μm, respectively.
 25. The flat metal workpieceaccording to claim 24, wherein the average roughness values Ra and Rzrange from 0.24 to 0.28 μm and 1.6 to 1.9 μm, respectively.
 26. The flatmetal workpiece according to claim 24, wherein the metal surface has anadhesive strength, as determined by the 180° peel test using an FR-4epoxy resin and expressed as peel strength in N/mm, of 1.5 N/mm orgreater.
 27. The flat metal workpiece according to claim 24 comprised ofa metal consisting of copper, tin, silver and iron or a metal alloycomprised of copper, iron, silver or tin.
 28. The flat metal workpieceaccording to claim 24 comprised of copper.
 29. The flat metal workpieceaccording to claim 24, where the metal balls deposited on the flat metalworkpiece are comprised of copper balls.
 30. The flat metal workpieceaccording to claim 29, which is a copper foil or a copper strip, thesurface of which having the peel strength of 1.5 to 3.0 N/mm.
 31. Theflat metal workpiece according to claim 27 wherein the metal aggregateslocated on the surface of said metal workpiece are additionallycomprised of lanthanoid.
 32. Flat metal workpiece produced by the methodaccording to claim
 14. 33. A composition of matter comprised of the flatmetal workpiece of claim
 27. 34. A composition of matter comprised ofthe flat metal workpiece of claim
 32. 35. The composition of matteraccording to claim 33 which comprises the flat metal workpiece bonded toa material selected from thermoplastics, synthetic resins, adhesives,lacquers and pastes.
 36. The composition of matter according to claim 34which comprises the flat metal workpiece bonded to a material selectedfrom thermoplastics, synthetic resins, adhesives, lacquers and pastes.